My Dad has the same heater and he claimed he'd get a 2 degree rise in temp/hr. I however got 2 degrees in about 8hrs (similar size pool). It would take me 30-40 minutes to heat my spa to 100 degrees and with the Sta-Rite it takes 12 minutes. While that is in part due to the extra 100K btu it is also running on the proper size pipe. All these years I was frustrated with the heater and had no idea why...........